Chemical monitoring method and apparatus, and incinerator

ABSTRACT

There was previously no monitoring method and monitoring apparatus which could measure dioxins at ppt levels and dioxin precursors at ppb levels with high sensitivity.  
     According to this invention, organic and inorganic compounds containing highly electronegative elements are selectively ionized by atmospheric pressure chemical ionization, the ions produced are detected by a mass spectrometer, and their amount is measured.  
     As a result, interfering substances such as nitrogen, air, hydrocarbons and carbon dioxide which are the main components of flue gas are eliminated, and dioxins or organochlorine compounds such as dioxin precursors can be selectively monitored.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a monitoring apparatus which measuresthe concentration of dioxins and related compounds such as dioxinprecursors in flue gas or the atmosphere by detecting dioxins andrelated compounds present in combustion gases from incineration ofdomestic waste and industrial waste, gases from metal refineries,automobile exhaust or the atmosphere. It relates also to a combustioncontroller which efficiently employs the results of monitoring incombustion.

[0002] When waste is incinerated in a garbage incineration plant, highlytoxic dioxins are produced in the flue gas. This gives rise toenvironmental pollution and is a serious social problem.

[0003] Dioxins are toxic to humans in various ways. Not only do theyhave acute toxicity, but they are also carcinogenic and teratogenic, andrecently, it has been shown that they act as “environmental hormones”,false hormones which disturb the internal secretions of the body.Dioxins are also known to be discharged in waste gases from metalrefining, exhaust from automobiles, or lye from bleaching processes.

[0004] The term “dioxins” is a general term referring to 75 isomers ofpolychlorinated dibenzene paradioxin (PCDDs) and 135 isomers ofpolychlorinated dibenzofuran (PCDFs), and in the wider sense includespolybisphenyl chlorides (Coplanar PCBs). Hereafter, dioxin and relatedcompounds will be referred to simply by the general term “dioxins”.

[0005] Although a great deal is known about the mechanisms by whichdioxins are produced (“Bunseki”, 1998, pp. 512-519), the conditionsunder which this occurs vary widely depending on location and mechanism,and are very complex. One of the leading factors is considered to bereaction between carbon and chlorine (de novo or new product synthesis)due to metal chlorides of cobalt, iron and copper which are present inthe ash of combustion processes under the high temperature ofincineration plants, and which act as catalysts. In the basic reactionof this de novo synthesis, when carbon atoms, chlorine atoms and oxygenatoms are present together at high temperature, they produce manyorganochlorine compounds such as dioxins, chlorobenzene and chlorophenolby radical reactions. It is said that this chlorobenzene andchlorophenol are themselves precursors of, and give rise to, dioxins.Formation of dioxins in a waste incineration plant is said to mainlyoccur in two places, i.e., a process which takes place during incompletecombustion in an incinerator when the incineration temperature is lessthan 800° C., and in a de novo synthesis in a boiler or dust filter at atemperature of 250° C. to 550° C.

[0006] Various policies have been devised to reduce the formation ofhighly toxic dioxins in an incinerator plant as much as possible. Toinhibit dioxin emission into the environment, techniques have beendevised to improve incineration conditions and remove dioxinefficiently. However, much time and effort were needed to develop thisinhibition technology. Specifically, garbage was incinerated undercertain conditions, the concentration of dioxins in flue gas or ashunder these conditions was determined, a correlation between combustionconditions and dioxin amount was found, and optimum incineratorconditions or dioxin removal conditions were then found from thiscorrelation.

[0007] To make an accurate measurement of dioxin concentration,reference must be made to the regulatory law concerning the assay ofdioxins. Generally, quantitative analysis of dioxins is carried out bythe technique shown on pp. 441-444 of Pharmacia Vol. 34, No. 5 (1998).This is done by complex pre-processing to separate only desiredcomponents from a sample taken from an incinerator under fixedconditions, and performing qualitative and quantitative analysis using acostly, large-scale high resolution mass analyzing device (having a massresolution of 10000 or more) installed in special equipment which doesnot release dioxins outside the system.

[0008] At the same time, many observation monitors are installed invarious parts of an incinerator such as a garbage incinerator to controlits operation while it is running. These include monitors for monitoringthe temperature of various parts of the incinerator, an oxygenconcentration monitor, a carbon monoxide monitor, a nitrogen oxide(NO_(x)) monitor, a sulfur oxide (SO_(x)) monitor, etc. These monitorsare used for monitoring and controlling combustion, but they may also beused indirectly as monitors for reducing dioxins as stated on pp. 89-92of Waste Incineration Technology (Ohm Co., 1995). Specifically, oxygenmonitors, carbon monoxide monitors and temperature monitors are observedso that flue gases are completely burnt, and formation of dioxins isinhibited as far as possible.

[0009] To monitor the operation of an incinerator, an alternative methodhas been proposed wherein, instead of attempting to measure theconcentration of dioxins directly which may be present in only very lowconcentrations, another substance present in relatively highconcentration is measured, and the concentration of dioxins is estimatedfrom the result. Examples of this technique and devices employing it aregiven in Yokohama National University Environmental Research Abstracts(Vol. 18, 1992), Japanese Patent Laid-Open No. Hei 4-161849, JapanesePatent Laid-Open No. Hei 5-312796, Japanese Patent Laid-Open No. Hei7-55731, Japanese Patent Laid-Open No. Hei 9-015229, and Japanese PatentLaid-Open No. Hei 9-243601.

[0010] In the technique disclosed by Yokohama National UniversityResearch Abstracts (Vol. 18, 1992), Japanese Patent Laid-Open No. Hei4-161849, and Japanese Patent Laid-Open No. Hei 5-312796, chlorobenzenesare measured by gas chromatography (GC), and are used as indicator fordioxins. The dioxins are estimated from the correlation between the two.

[0011] In the technique shown in Japanese Patent Laid-Open No. Hei7-155731, dioxins in combustion ash are thermally decomposed by heattreatment of the ash, and dioxins are thereby inhibited. Chlorobenzenesor chlorophenols present in the ash before and after heating areanalyzed, and a dioxin elimination factor is estimated. In this way,thermal decomposition conditions can be optimized.

[0012] In the technique shown in Japanese Patent Laid-Open No. Hei9-015229, the concentrations of chlorobenzene and chlorophenol in fluegas are measured, and the dioxin concentration is found from thistogether with a dust concentration and flue gas retention time which aremeasured separately.

[0013] In the technique shown in Japanese Patent Laid-Open No. 9-243601,chlorobenzenes and chlorophenols in flue gas are measured in real time,and the dioxin concentration is measured continuously. Theconcentrations of chlorobenzenes and chlorophenols are found by leadingflue gas into a laser ionization mass spectrometer, ionizing the gas andperforming a mass analysis. As a result, the dioxin concentration isfound indirectly.

[0014] It was hoped that the formation of dioxins and their emissionfrom garbage incineration plants would be reduced by these attempts toimprove combustion conditions or use of eliminating techniques. However,it is necessary to measure, in real time, how much dioxin has actuallybeen reduced by adoption of these curtailment policies. From thisviewpoint, the following problems are inherent in the conventionalmethods mentioned above.

[0015] Although precise analytical results for dioxins, including typesof isomers and their amount, can be obtained from the mandatory methodsfor its assay, the analysis itself is extremely complex. In addition,special equipment to avoid releasing dioxins outside the system and acostly, bulky, high resolution magnetic mass spectrometer are necessary,and skilled measurement techniques are required. Consequently, theanalysis of dioxins cannot be conducted in the incineration plant “onsite”, which meant that ash samples or gas samples had to be sent to ananalysis center, the analysis took almost a week, and the cost involvedper sample was of the order of several hundred thousand yen.

[0016] There is very little correlation between the numerical valuesobtained by observation monitors currently employed to control theoperation of garbage incinerators, such as oxygen monitors, carbonmonoxide monitors, temperature monitors, nitrogen oxide (NO_(x))monitors and sulfur oxide (SO_(x)) monitors, and the concentration ofdioxins. Therefore, it was impossible to know whether or not emission ofdioxins was being suppressed, or how much dioxins were being discharged,while an incinerator was operating. Hence, from these indirect monitors,even an estimate of dioxin concentration could not be obtained.

[0017] In the techniques indicated by Yokohama National UniversityEnvironmental Research Abstracts (Vol. 18, 1992), Japanese PatentLaid-Open No. Hei 4-161849 and Japanese Patent Laid-Open No. Hei5-312796, a minimum of 30 minutes to 1 hour is needed for measurementapart from trapping and concentration time. Moreover, it was difficultto selectively detect chlorobenzenes in the organic compounds which arepresent in large quantities in flue gas, and there was also apossibility of erroneous measurements due to interfering substances.

[0018] In the technique disclosed by Japanese Patent Laid-Open No. Hei7-155731, specific techniques such as for as on-line sample introductionand automatic measurement are not described, and the measurement itselfrelied on conventional methods such as GC which required about 20 or 30minutes per sample apart from the extraction operation.

[0019] In the technique disclosed by Japanese Patent Laid-Open No. Hei9-015229, a clear basis is not given for the relation between dioxins,chlorophenols and chlorobenzenes which is assumed in the invention, andthe determination of chlorobenzenes and chlorophenols was performed bythe conventional methods which take time such as gas chromatography.

[0020] The technique shown in Japanese Patent Laid-Open No. Hei 9-243601discloses the possibility of real-time concentration measurement ofchlorobenzenes, but in this multiphoton ionization, there is said to bea decrease of sensitivity of from {fraction (1/7)} to {fraction (1/10)}for each additional chlorine atom substituted in the benzene nucleus.Trichlorobenzene is ionized with an efficiency of only about {fraction(1/100)} of that of monochlorobenzene, i.e., it can be said that thesensitivity to trichlorobenzene is only {fraction (1/100)} that ofmonochlorobenzene. 2,3,7,8 tetrachlorodibenzene-p-dioxin (2,3,7,8-TCDD), which is known to be the most toxic dioxin, is a dioxinwherein four hydrogens at positions 2, 3, 7 and 8 are replaced bychlorine. Moreover, all other toxic dioxins are compounds substituted byfour or more chlorine atoms. If this highly toxic dioxin is synthesizedfrom chlorobenzenes and chlorophenols, a chlorobenzene or chlorophenolwith two, three or more chlorine atoms must be the precursor material.However, in the multiphoton ionization described in this publication, itis difficult to efficiently ionize polysubstituted chlorine compounds.In other words, it was extremely difficult to measure organochlorinecompounds such as chlorophenols at a concentration of 1000 ng/Nm³ whichare said to be present in incinerator flue gas.

SUMMARY OF THE INVENTION

[0021] In order to solve the above-mentioned problems, this inventionprovides a monitor equipped with a sampling system for sampling flue gasand the atmosphere, an ion source for ionizing trace compounds in thesample gas at atmospheric pressure or a pressure close to atmosphericpressure, a mass analyzing part for mass analysis of ions produced bythis ion source and measuring its ion current, and a data processor forprocessing measured signals. As ions can be detected rapidly by massanalysis, monitoring can be performed in real-time.

[0022] In this monitor, the tendency of dioxins, chlorobenzenes andchlorophenols to form negative ions is fully exploited. First, samplegas containing hydrocarbon molecules from the incinerator is led to theion source using a pipe which is heated to prevent adhesion. In this ionsource, trace compounds in the sample gas are selectively ionized by anegative corona discharge under a predetermined pressure to formnegative ions. These negative ions are analyzed by mass spectrometry,then a qualitative determination of the sample gas is performed from themass numbers of the observed ions and a quantitative determination ofthe sample gas is performed from the ion amount. In atmospheric pressurechemical ionization, unlike the conventional laser ion method, theionizing efficiency does not depend much on the number of chlorineatoms, so dioxins, or dioxin precursors (chlorobenzenes orchlorophenols) with different numbers of chlorine atoms can be detectedwith high sensitivity. This means that components such as dioxins ordioxin precursors can be monitored. Further, a negative ion is formed bydeprotonation from the dioxin precursors in flue gas. This negative ionis introduced to a three-dimensional quadruple mass spectrometer to forma negative ion wherefrom one chlorine atom has been eliminated. Themethod makes it possible to predict the dioxin generation amount byselectively performing mass analysis on particular decompositionproducts from dioxin precursors in the negative ions which are produced.

[0023] Therefore, dioxins or dioxin precursors present at lowconcentrations in flue gas can be detected with high sensitivity andrapidity using an ion trap mass spectrometer which traps the ions usinga high frequency electric field, and then performs mass analysis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a diagram showing the construction of a flue, monitorand combustion controller.

[0025]FIG. 2 is a diagram showing the construction of the flue andmonitor.

[0026]FIGS. 3A, 3B are diagrams showing the construction of a filter.

[0027]FIG. 4 is a diagram showing the external appearance of themonitor.

[0028]FIG. 5 is a diagram showing a typical construction of the monitorinterior.

[0029]FIG. 6 is a diagram showing another construction of the monitorinterior.

[0030]FIG. 7 is a diagram showing a typical construction of an ionsource.

[0031]FIG. 8 is a diagram showing another construction of the ionsource.

[0032]FIG. 9 is a diagram showing yet another construction of the ionsource.

[0033]FIG. 10 is a diagram showing a corona discharge ion generationprocess.

[0034]FIG. 11 is a diagram showing the construction of an ion trap massanalyzing part.

[0035]FIG. 12 is a diagram describing the construction of the ion trapmass analyzing part.

[0036]FIGS. 13A, 13B are diagrams showing an ion generation process.

[0037]FIGS. 14A, 14B are diagrams showing constructions of a dustfilter.

[0038]FIG. 15 is a diagram showing monitor observation points.

[0039]FIG. 16 is a diagram showing a typical arrangement of the monitor.

[0040]FIG. 17 is a diagram showing another arrangement of the monitor.

[0041]FIG. 18 and FIG. 19 are diagrams showing other arrangements of themonitor.

[0042]FIG. 20 is a diagram showing a relation between gas temperatureand ion intensity in an atmospheric pressure ion source.

[0043]FIG. 21 is a diagram showing a relation between gas temperatureand ion current in the atmospheric pressure ion source.

[0044]FIG. 22 is a diagram showing a relation between pressure and ionintensity in the atmospheric pressure ion source.

[0045]FIG. 23 is a diagram showing a relation between pressure and ioncurrent in the atmospheric pressure ion source.

[0046]FIG. 24 is a diagram showing a typical mass spectrum.

[0047]FIG. 25 is a diagram showing a typical mass spectrum of achlorobenzene.

[0048]FIG. 26 is a diagram showing a typical mass spectrum of a dioxin.

[0049]FIG. 27 is a diagram showing an example of detection ofchlorophenols.

[0050]FIG. 28 is a diagram showing an example of measurement of asensitivity curve.

[0051]FIG. 29 is a diagram showing an example of measurement of acalibration line.

[0052]FIG. 30 is a diagram showing the main components of flue gas.

[0053]FIGS. 31A, 31B and 31C are respectively diagrams showing detectedions.

[0054]FIG. 32 is a diagram showing an example of the operation of amonitor.

[0055]FIG. 33 is a diagram showing an example of a measurement sequencefor dioxins.

[0056]FIG. 34 is a flowchart of a typical measurement sequence.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] (Embodiment 1)

[0058]FIG. 1 is a diagram showing the construction of a monitoringsystem according to one embodiment of this application. This systembasically comprises a gas sampling unit 88 (inside the dotted line inFIG. 1) for sampling gas from a flue 1 which is to be measured, amonitor 11 for detecting substances to be measured in the sample gas,and a combustion controller 15 for utilizing the detection results incombustion control.

[0059] The sampling unit 88 comprises a gas sampling probe 3, sample gaspipe 4, change-over valve 6, filter 7, gas blow pump 8, waste gas pipe5, and waste gas probe 2. As a whole, the sample gas introduction systemhas the function of sending sample gas to the monitor regularly withoutloss of substances to be measured due to adhesion and condensation, andat a fixed flowrate. For this purpose, although not illustrated, thewhole of the sampling unit 88 is heated to from 100 degrees C. to about300 degrees C. by a wire heater. This heating temperature varies withthe substances to be measured. To keep the sampling unit warm, it iseffective to surround the sample gas pipe 4, for example, with aninsulating material. In the monitor 11, the substances to be measuredare detected (monitored) by selectively and efficiently ionizing thesesubstances in the sample gas introduced, and performing mass analysis ofthe ions produced in the mass analysis part.

[0060] The detected signal is sent to the data processing part where itis converted to a concentration from a calibration curve, and output toa CRT or printer as data. It is also sent to the combustion controller15 as data for combustion control of the incineration plant via signaland control lines 14. Further, an instrument part 13 is providedcomprising observation monitors such as an oxygen monitor, carbonmonoxide monitor, temperature monitor, nitrogen oxide (NO_(x)) monitor,sulfur oxide (SO_(x)) monitor and hydrogen chloride monitor, andcombustion is controlled by the monitor 11 in view of the resultsobtained.

[0061] In FIGS. 2 and 3A, 3B, the gas sampling part 88 and monitor 11are shown enlarged. When gas is sampled, the gas sampling probe 3 whichhas a sampling port 89 upstream of the flow of flue gas is inserted inthe flue 1. A change-over valve 6 is provided after the gas samplingprobe 3 to control the introduction of sample gas to the monitor 11. Thesample gas pipe 4 is used to transport the sample gas, and this isheated to from 100 degrees C. to about 300 degrees C. by a wire heater,not shown, to prevent adsorption and condensation of the substances tobe measured on the pipe wall. Temperature unevenness can be reduced bywinding a heat insulating material around the whole piping. The bore ofthe sample gas pipe 4 depends on the flowrate of sample gas to be passedthrough it, but it is of the order of 1 mm to 100 mm.

[0062] The sample gas is introduced to the filter 7 where solidimpurities and ash in the sample gas are removed. FIG. 3 shows anenlargement of the filter 7. The diagram shows a case where two kinds offilter, i.e., a dust filter 20 and metal filter 23, are provided midwayalong the sample gas pipe 4. In FIG. 3A, the dust filter 20 a comprisesa dust filter inlet pipe 21, a dust filter outlet pipe 22 and silicawool 19 a packed in the dust filter. The tip of the dust filter inletpipe 21 is led close to the base of the dust filter so that the samplegas is bound to come in contact with the silica wool 19 a packed thereinby the time the gas leaves the dust filter outlet pipe 22. The silicawool 19 a is gradually contaminated by the gas, and is replaced whennecessary. Also, a dust filter 20 b filled with silica wool 19 b may bearranged horizontally as in FIG. 3B, and if the construction is suchthat the interior may be observed, the state of contamination can beeasily determined and the time when the silica wool should be replacedcan be known.

[0063] To reduce adsorption of sample gas by the silica wool 19 in thedust filter 20 which does not easily transmit temperature, the wallsurface temperature of the dust filter 20 must be raised above thetemperature of the sample gas pipe 4. For example, when measuring dioxinprecursors such as chlorobenzenes and chlorophenols, and the sample gaspipe 4 is at about 120 degrees C., it is effective to increase thetemperature of the dust filter 20 to about 180 to 200 degrees C. Manysolid impurities, ash, etc. can be removed by the dust filter 20, but ifa metal filter 23 is provided thereafter, influx of still finer dust tothe monitor 11 can be prevented. The size of the dust removed may becontrolled by the mesh of the metal filter, and is often of the order ofseveral micrometers. This part is also replaceable. Depending on theamount of solid impurities or ash at the gas sampling points, two orthree of these filters may be combined. In such a case, prolongedmonitoring is possible if the mesh of the filters is arranged to beprogressively finer from upstream to downstream of the gas samplingpoints in the pipe. To prevent corrosion by flue gas, it is desirablethat pipes and valves are made from stainless steel or titanium which donot easily corrode. To prevent components present in very small amountsfrom adsorbing to the wall surface of the piping, it is desirable to usea polytetrachloroethylene lined pipe or a glass lined pipe. Instead of aglass lined pipe, piping may be packed with glass tubes or quartz tubescut to short lengths. A wide bore fused silica column used as a gaschromatography (GC) column may also be employed.

[0064] It is convenient if the aforesaid sample gas preprocessing partis provided with plural lines which can be changed over. That is, whenone of the dust filters 20 is clogged with ash, etc., the line can bechanged over to another of the filters 20, and the filter clogged withash cleaned while measurements are continued.

[0065] Sample gas is introduced into the monitor 11 by the gas blow pump8. The flowrate of sample gas introduced depends on the bore and lengthof the sample gas pipe, and the blowing speed of the pump 8, but it isof the order of 1-300 liter/minute. A mechanical pump such as adiaphragm pump may be used for the pump 8, but it is important to beable to heat the parts in contact with sample gas to some extent toprevent adsorption of the sample in the pump parts. Dioxin and itsrelated compounds exist in flue gas only in minute amounts. Thesecompounds are easily adsorbed to the wall surface of sampling systemssuch as pipes and filters, etc. To prevent this adsorption as much aspossible, therefore, the whole sampling system is heated as mentionedabove, or pipes are made of materials with low adsorption. Adsorptioncan be reduced if the amount of flue gas flowing in the piping isincreased. That is, the residence time of flue gas in the piping isshortened as much as possible.

[0066] Moreover, when there is a difference in the sample gas amountflowing through the pipe 4 and an optimum sample gas amount which shouldflow into the monitor 11, a branch valve 9 may be formed as shown inFIG. 1 to control the gas amount flowing into the monitor 11.

[0067] Next, the sample gas is introduced into the monitor 11. FIG. 4and FIG. 5 respectively show the external appearance of the monitor 11and the detail of the interior of the monitor 11. In order to installthe analysis mainframe of the monitor 11 outdoors near the flue, it isplaced in a well-sealed monitor rack 90 whereof temperature control isperformed to some extent (approximately 10 to 50 degrees C.). Themonitor rack 90 is fixed by a monitor support 28. An atmosphericpressure chemical ionization ion source housing 26 for ionizing thesample gas is installed in such a way that it can be easily dismantledto facilitate periodic cleaning of the ion source. Also, as will bedescribed later, it is preferable to place a vacuum pump 12 whichradiates a large amount of heat outside the monitor rack 90, as shown inFIG. 4. As mentioned above, the filter 7 is installed midway along thesample gas pipe 4, but in view of fine dust which has passed through itflowing into the interior of the mass analysis part, it is preferable toprovide a dust filter housing 27 in a vacuum tank. The data measured bythe monitor 11 are transmitted to the combustion controller 15 via thesignal and control line 14.

[0068] An arrangement may be made so that the results on the CRT orprinter may also be observed on the monitor 11 via an observation window18 of the monitor. Also, by providing a standard sample generator 10,periodic inspection of monitor performance can be made via a standardsample change-over valve 24 and a standard sample pipe 25. That is, astandard gas is periodically introduced instead of flue gas, and it isconfirmed whether or not ions from the standard gas are observed to beequal to or greater than a fixed amount. If the ion intensity observedis below the fixed amount, maintenance is performed.

[0069] The sample gas is then sent to a atmospheric pressure chemicalionization ion source 30 shown in FIG. 5. FIG. 7 shows an enlargement ofthe ion source 30. A high voltage (from about −3 kv to −7 kv) is appliedto a corona discharge needle electrode 57 in a discharge counterelectrode 58. The temperature of this area is kept at approximately 50to 300 degrees C. by a heater, not shown. The distance between thecorona discharge needle electrode 57 and discharge counter electrode 58is about 1 to 10 mm. Due to the negative corona discharge at the tip ofthe needle electrode as a result of applying the high voltage,ionization of dioxins and dioxin precursors takes place. The details ofthis ionization due to the negative corona discharge may be described asfollows. Dioxins and related substances have elements with highelectronegativity in the molecule, such as a large number of chlorineatoms, oxygen atoms, etc., (Group VI and Group VII of Periodic Table).That is, they are organochlorine compounds. A toxic dioxin is a dioxinhaving from four to eight chlorine substitutions. These compounds easilytrap low energy thermoelectrons to become negative ions. On the otherhand, there is no ionization process wherein hydrocarbons which occur inlarge quantities in flue gas trap thermoelectrons to become negativeions. Therefore, even if hydrocarbon molecules are present in largequantities in sample gas, they do not become negative ions.Thermoelectrons can be produced in large quantities by corona dischargein the atmosphere, as shown in FIG. 10, and if a negative high voltage(approximately −3 kV to −7 kV) is applied to the needle-like coronadischarge electrode 57, a corona discharge will start at the tip of thecorona discharge electrode 57. Specifically, primary electrons due tothis corona discharge are emitted from the tip of the corona dischargeelectrode 57. These primary electrons due to corona discharge areaccelerated by the high voltage applied to the discharge electrode, andcollide with surrounding atmospheric molecules (nitrogen and oxygen) togive. rise to large numbers of secondary and tertiary electrons. Thesesecondary, tertiary and quartenary electrons then suffer repeatedelastic collisions with neutral molecules, so their energy graduallydecreases, and they finally attain a resonance capture energy (2 ev orless). Consequently, the thermoelectrons which are produced in largeamounts around the corona discharge electrode 57, are selectivelycaptured by organochlorine compounds, such as dioxins, chlorobenzenesand chlorophenols. Oxygen captures a thermoelectron to form a O₂ ⁻ ion.This ion collides with a dioxin or related compound, supplies a chargeto an organochlorine compound which more easily becomes a negative ion,or reacts with an organochlorine compound to form these negative ions.Therefore, even if oxygen is present in flue gas or the atmosphere to aconcentration of 100 ppm or more, it does not interfere with theformation of negative ions. In an atmospheric pressure ionizationprocess, water forms an OH⁻ ion. This OH⁻ ion collides with a dioxin oran organochlorine compound, and the negative charge is transferred tothe dioxin or organochlorine compound, or withdraws a proton (H⁺) from aneutral molecule to form a negative ion. Hence, there is a considerableadvantage in using a negative corona discharge for ionizingorganochlorine compounds, such as dioxins, chlorobenzenes andchlorophenols.

[0070] Water molecules which are present in large amounts in flue gascollide with the negative ions produced, and plural water molecules bondwith the negative ions to form cluster ions. If the mass of a naked ionis M, and if the number of added water molecules is n, the mass of thiscluster ion will be (M+18n). 18 is the molecular weight of water. Theformation of cluster ions not only interferes with the analysis, butmakes a high sensitivity measurement impossible. The formation of thesecluster ions is promoted by cooling the molecules or ions, therefore aneffective means of suppressing cluster ions is to maintain the ionsource 30 at from about 50 to 500 degrees C., and preferably in therange of from about 100 to 300 degrees C. Heating may be performed byproviding a heater to each part, or by providing a sample gas heaterunit 62 and heating the sample gas directly by a heater 63 comprisingmultiple coils of metal wire wound therein, as shown in FIG. 9. Theimportance of this may also be seen from the data shown in FIGS. 20 and21. FIG. 20 shows the relation of the temperature of the sample gas tothe ion intensity obtained when the gas is heated by the sample gasheater unit 62. It is seen that when the gas temperature rises, the ionintensity rises abruptly, the variation above 100 degrees C. beingparticularly remarkable. FIG. 21 shows the difference of ion intensityobtained when the temperature of the gaseous sample is (a) 150 degreesC. and (b) 30 degrees C. It is seen that when heating is performed, thecurrent increases by about 2.5 times compared to the case where heatingis not performed for the same corona discharge voltage (−2.5 kv).Current stability is also much better when heating is performed. If thesample gas is at high temperature, for example, if it has reached 100degrees C. or more, the moisture in the gaseous sample introduced willalso evaporate and ionization by corona discharge will proceedefficiently and stably.

[0071] The details of the mass analysis part, etc., will now bedescribed using FIGS. 5 and 7. Mass spectrometers of various kinds canbe used in analyzing the ions which are produced, but below, the case isdescribed where an ion accumulating type ion trap mass spectrometer isused. The situation is the same when a quadruple mass spectrometer whichperforms a mass separation using the same high frequency electric field,and a magnetic field type mass spectrometer using mass variance in amagnetic field, are employed.

[0072] The negative ions produced by the corona discharge at the tip ofthe corona discharge needle electrode 57 pass through a first aperture59 (diameter approximately 0.3 mm, length approximately 0.5 mm) in afirst flange 31 of a differential pumping region, a second aperture 60(diameter approximately 0.3 mm, length approximately 0.5 mm) in a secondflange 32 and a third aperture 61 (diameter approximately 0.3 mm, lengthapproximately 0.5 mm) in a third flange 33 which are heated by a heater,not shown. These apertures are heated by the heater to about 100 to 200degrees C. A voltage is applied between the first aperture 59 and secondaperture 60, and between the second aperture 60 and third aperture 61,which increases ion transmission efficiency. At the same time, clusterions formed by adiabatic expansion are declustered due to collision withremaining molecules so as to produce ions of the sample molecules. Thedifferential pumping region is usually evacuated by a robust pump suchas a rotary pump, scroll pump or a mechanical booster pump. Aturbomolecular pump may also be used to evacuate this area. The pressurebetween the second aperture 60 and the third aperture 61 is in the rangeof 0.1 to 10 Torr. It is also possible to construct the differentialpumping region using two apertures, i.e., the first aperture 59 andthird aperture 61, as shown in FIG. 8. However, as the gas amountflowing in increases as compared with the above-mentioned case, theevacuation rate of the vacuum pump used must be increased and thedistance between the holes must be increased. In this case also, it isimportant to apply a voltage between the two apertures.

[0073] After the ions so produced have passed through the third aperture61, they are focused by a focusing lens 34. An Einzel lens comprisingthree electrodes is usually used for this focusing lens 34. The ionsthen pass through an electrode 35 with a slit. Due to the focusing lens34, the ion which have passed through the third aperture 61 are focusedon this slit. Dust which is not focused collides with this slit part andseldom enters the mass analysis part. After the ions have passed throughthe electrode 35 with the slit, they pass through a gate valve 36, areagain focused by a double cylinder type focusing lens 91 comprising aninner cylindrical electrode 37 and outer cylindrical electrode 38 havinga large number of openings, and are deflected by about 90 degrees by adeflector 92 comprising deflector electrodes 40 a, b, c, d (acylindrical electrode split into four parts) situated inside a screeningelectrode 39 to eliminate the effect of external voltages. In the doublecylinder type focusing lens 91, the ions are focused using the electricfield of the outer cylindrical electrode 38 which spreads out from theopenings of the inner cylindrical electrode 37. The reason why the ionsare deflected at about 90 degrees is so that only ions are introducedinto the mass analysis part, dust or other particles flowing into thevacuum from the third aperture 61 being ejected straight ahead toaccumulate in a dust filter 43 in a vacuum tank. The dust filter 43 inthe vacuum chamber may be (a) a cylindrical type or (b) a 90° curvedtype as shown in FIGS. 14A, 14B. In the case of the curved type, whendust accumulates at the bottom, cleaning may be easily performed byremoving the flange 71 b.

[0074] After the ions which pass through the deflector 92 are focused bya cylindrical electrode 44, they are introduced into an ion trap massanalyzing part 93. FIG. 11 shows an enlargement of the ion trap massanalyzing part 93 comprising a gate electrode 65, endcap electrodes 45a, b, a ring electrode 46, collar electrodes 66 a, b, insulating rings68 a, b, and an ion extracting lens 70. The gate electrode 65 has thefunction of preventing ions outside from entering the ion trap massanalyzing part 93 when ions trapped in the mass analyzing part areremoved from the system. As shown in FIG. 12, ions introduced to themass analyzing part 93 collide with a buffer gas such as heliumintroduced into the mass analyzing part 93, and their orbit becomessmall. They are then ejected from the system, each mass number in turn,by scanning with a high frequency voltage applied by a high frequencypower supply 100 between the endcap electrodes 45 a, b and the ringelectrode 46, and pass through the ion extracting lens 70 to be detectedby an ion detector 94. The pressure in the mass analyzing part 93 whenthe buffer gas is introduced is of the order of 10⁻³ to 10⁻⁴ Torr. Themass analyzing part 93 is controlled by a mass analyzing part controller51 (FIGS. 5 and 6). One of the advantages of an ion trap massspectrometer is that it has the ability to trap ions, and it cantherefore detect ions even at low sample concentrations if theaccumulating time is made longer. Therefore, even if the sampleconcentration is low, ions can be concentrated by a high factor in themass analyzing part 93, and this very much simplifies samplepreprocessing, e.g. concentration.

[0075] If the magnitude of the high frequency voltage applied by thehigh frequency power supply 100 between the endcap electrodes 45 a, band the ring electrodes 46 is set to a certain value while introducingions into the mass analyzing part 93, a cut-off (low mass ion cutoff) ofthe ion mass numbers trapped between the endcap electrodes 45 a, b andthe ring electrode 46 can be achieved. This means that ions smaller thana certain mass are not trapped within the electrodes. In the low massnumber region below 100, there are large numbers of ions derived fromwater, hydrogen chloride, NO_(x), SO_(x), etc. If these ions are nottrapped in the endcap electrodes 45 a, band the ring electrode 46,saturation of ions in the electrodes can be prevented, and dioxins ororganochlorine compounds which have large mass numbers can beefficiently trapped in the electrodes, as shown in FIGS. 31A to 31C.Further, unnecessary ions with large mass can be eliminated from theelectrode by controlling the frequency of an auxiliary alternatingvoltage applied between the endcap electrodes 45 a, b from auxiliaryalternating current power supplies 98 a, 98 b shown in FIG. 12. Inpractice, a white noise auxiliary alternating current which does notcontain the resonant frequency of the ions to be trapped by the massanalyzing part 93 is applied to the endcap electrodes 45 a, b. The massanalyzing part 93 traps and accumulates only ions of target mass withinthe electrodes. Therefore, target molecular ions and fragment ions areefficiently accumulated and detected. In addition to the selectivity ofthe atmospheric pressure chemical ionization method, the furtherimprovement of selectivity and sensitivity provided by the ion trap massspectrometer makes it possible to detect organochlorine compoundsincluding dioxins.

[0076] In the detection of ions extracted from the mass analyzing part93, the ions are converted to electrons by a conversion dynode 48, andthese electrons are detected by a scintillation counter 49, as shown inFIGS. 5 and 6. The signal obtained is amplified by an amplifier 50, andsent to a data processor 47.

[0077] A chamber containing the focusing lens 34, the electrode with aslit 35, the double cylinder type focusing lens 91, the deflector 92,the cylindrical electrode 44, the mass analyzing part 93 and the iondetector 94 as shown in FIGS. 5 and 6, is evacuated to approximately10⁻⁴ to 10⁻⁶ Torr (at a rate of about 50 to 200 liter/second on the sideof a second differential pumping region evacuation pipe 55 and a rate ofabout 50 to 150 liter/second on the side of a third differential pumpingregion evacuation pipe 56) by a split flow type turbomolecular pump 52.

[0078] In this regard, it is convenient to split the vacuum chamberafter the gate valve 36 into two parts at the deflector 92, and evacuatethe chamber split into two via the second differential pumping regionevacuation pipe 55 and third differential pumping region evacuation pipe56 using one split flow type turbomolecular pump 52, as shown in FIG. 5.This is convenient for the following reasons. Firstly, the massanalyzing part 93 is not easily contaminated by dust, etc. In addition,when the gate valve 36 is closed, the first to third apertures 61 areset at atmospheric pressure and the ion source 30 and differentialpumping region are cleaned, the ion trap mass analyzing part 93 can bekept under vacuum, so the monitor 11 can be rapidly reinstated withinabout 1 or 2 hours after cleaning. The auxiliary vacuum pump 12 must beprovided to the turbomolecular pump 52 on the back pressure side. Thismay be used in conjunction with the pump used for the differentialpumping region, in which case a valve 53 is provided midway in a firstdifferential pumping region evacuation pipe 54. In this embodiment, ascroll pump with a evacuation rate of approximately 500 liter/minute isused as the auxiliary vacuum pump 12. Further, a robust vacuum pumpconnected to the first differential pumping region evacuation pipe 54can be made separate from the auxiliary vacuum pump 12 of theturbomolecular pump 52 via vacuum evacuation pipes 29 a, b as shown inFIG. 6. In this case, a pump with a small evacuation rate ofapproximately 100 liter/minute may be used as the auxiliary vacuum pump12 of the turbomolecular pump 52. In both of the cases shown in FIGS. 5and 6, the use of this type of arrangement simplifies the vacuum pumpingsystem of the atmospheric pressure chemical ionization mass spectrometerwhich tends to be very complex. In the examples of FIGS. 5 and 6, thecase was shown of three stage differential pumping region, but if thegas flowrate in the first to third apertures 61 is suppressed, a twostage differential pumping system may also be used.

[0079] The detected ion current is sent to the data processor 47 via theamplifier 50, and a mass spectrum is thereby obtained. An example of themass spectrum obtained by the atmospheric pressure chemical ionizationmethod of the present application is shown in FIG. 24 (NO₂ ⁻, NO₃ ⁻,etc.), FIG. 25 (case of 1,2,3-trichlorobenzene), and FIG. 26 (case of1,2,3-trichlorodibenzo-para-dioxin). These spectra show ion currents (Yaxis) corresponding to the mass numbers (X axis) of ions of componentsto be monitored. In the case of 1,2,3-trichlorobenzene, and1,2,3-trichlorodibenzo-para-dioxin, plural isotope peaks are observed inthe molecular ion part. This is due to the stable isotopes of thechlorine atom (³⁵C and ³⁷C, intensity ratio being 76:24). Themeasurement of the mass spectrum is usually completed in a short time ofabout 1 second to several tens of seconds. Mass spectrum measurementsmay also be repeated, and an average of the spectra taken to improve theS/N ratio.

[0080] From the ion current for the mass number due to the substance tobe measured, and a relation (calibration curve) between the amount andion current of a standard substance prepared beforehand, the amount of atarget substance can be calculated. For example, in the case of2,3-dichlorophenol (molecular weight 162, observed ion mass number 161),a variation of ion intensity relative to concentration in the sample gasis measured as shown in FIG. 28, and a calibration curve shown in FIG.29 is drawn. Based on this, concentration data in the sample gas at thattime are estimated from the observed ion intensity. The obtained dataare processed further, the concentration of the component is storedtogether with other parameters, and is output to a CRT or printer asnecessary.

[0081] Chlorobenzenes which are precursors of dioxins capture oneelectron to produce a molecular ion M⁻. Herein, a neutral molecule isrepresented by M, and a molecule which has captured an electron tobecome a negative ion is represented by M⁻. Chlorophenols lose oneproton of a phenoxy group (—OH group) to give the pseudomolecular ion(M−H). Dioxins give (M−C1)⁻ and (M−C1+O)⁻ apart from the molecular ionM⁻, and they also undergo fragmentation to give a 1,2 orthoquinone typefragment ion. If these characteristic peaks are selectively detected, ahigh selectivity, high sensitivity measurement can be made.

[0082] The molecular weights and monitored ions of chlorobenzenes,chlorophenols and dioxins are shown in FIGS. 31A to 31C. As the naturalisotopes of chlorine, 35 and 37, exist in the ratio of 3:1, the numberof chlorine atoms contained in an ion can be estimated by observing thisisotope pattern. Moreover, if plural isotope peaks are monitored andintegrated, high precision monitoring is possible. For example,trichlorobenzene gives an isotope pattern of 27:27:9:1 to masses 180,182, 184 and 186. If these ions are integrated, a high S/N ratio will beobtained as compared with the case when they are separate. In an actualmeasurement, all the ions in these tables may be monitored and thedioxin concentration estimated from their total amount, or only some ofthese ions may be monitored. For example, if only the ions present inlargest amounts are monitored, simple, high sensitivity monitoring canbe performed. Alternatively, if ions with 2 to 4 chlorine substitutionswhich contribute largely to the formation of dioxin are selectivelymonitored, simple, high precision monitoring can be performed.

[0083] In order to estimate the dioxin concentration from theconcentration of chlorobenzenes and chlorophenols, a correlation betweenthe two is used which is calculated beforehand. As the correlationdiffers somewhat depending on the type and model of incinerator, it isdesirable to determine this correlation for every incinerator where amonitor is installed.

[0084] As shown in FIGS. 1 and 2, flue gas which has passed through theion source 30 is passed through the waste gas pipe 5 by a waste gas pump95 (diaphragm pump), and is returned downstream of the gas samplingprobe 3 from the waste gas probe 2. This is so as not to dischargenoxious flue gas indoors during measurement. The gas discharged by thevacuum pump 12 of the mass spectrometer is also collected by a vacuumpump waste gas pipe 96 (FIG. 2), and returned to the flue 1 togetherwith flue gas which has passed through the ion source 30. The samplingpart 88 and ion source 30 are made airtight to prevent leakage to theexterior, prevent entry of the atmosphere, and prevent disturbances.

[0085] The flue gas contains water, hydrogen chloride, sulfur oxides,high boiling components and tar, etc. in large amounts, and ifcondensation, adsorption or corrosion due to these substances has anadverse effect on measurements, it is effective to remove them by animpinger inserted into the pipe system.

[0086] In the description given so far, when a sample gas was introducedinto the monitor 11, the gas blow pump 8 was provided upstream. As shownin FIG. 17, the flowrate of sample gas introduced into the ion source isdetermined to be from several liters/minute to several tens ofliters/minute by the blowing capacity of the gas blow pump 8, the needlevalves 79 a, 79 b and the resistance of the branch pipe 80, and thepressure in the ion source can be increased by controlling the needlevalves 79 a, b. Normally, in an atmospheric pressure ion source whichuses corona discharge, excess gas which does not flow in from the holeswhich take ions into the vacuum is expelled outside the ion source, sothe corona discharge area is effectively at atmospheric pressure(approximately 760 Torr). Actually, the ionization efficiency increasesto the extent that the molecular density in the corona discharge area ishigher, and the optimum value of the pressure of the corona dischargearea is higher than the atmospheric pressure of 760 Torr. However, ifthe pressure in the vicinity of the holes which take ions into thevacuum is too high, too many molecules will flow into the mass analysispart high vacuum through the holes, and it is difficult to maintain thehigh vacuum in the mass analysis part. FIG. 22 shows a relation betweenion source pressure and ion intensity. It is seen that in the maximum ofion intensity occurs at a higher pressure than 760 Torr. FIG. 23 shows asensitivity comparison between the case when the measurement isperformed when the pressure of the corona discharge area is increased(approximately 1.2 atmospheres), and the case when the measurement isperformed under effectively atmospheric pressure (approximately 1atmosphere). The sensitivity is approximately three times higher in theformer case than in the latter, showing that it is effective to increasethe pressure in the ion source 30. To control the pressure inside theion source, a pressure adjusting part may also be provided before theneedle valve 79 a, and the pressure of the corona discharge area of theion source 30 controlled by this pressure adjusting part 97 while thepump 8 is operating.

[0087] Alternatively, only a discharge pump 78 may be provided after themonitor 11 as shown in FIG. 16 to control the flowrate of sample gasentering the ion source 30 of the monitor 11 from several liters/minuteto several tens of liters/minute. In this case, the flowrate isdetermined by the discharge rate of the pump 78, the needle valves 79 a,b and the resistance of the branch pipe 80. It also possible to dispensewith the branch pipe 80.

[0088]FIG. 33 shows a flowchart for the measurement of dioxins. The gainof the detecting system is set to the highest sensitivity. Moreover, theion introduction time is made as long as possible (from about several100 msecs to several 10 secs). The ions derived from dioxins shown inFIG. 31C are monitored one after another. It is not necessary to monitorall the ions shown in FIG. 31C, and the number monitored can be reduced.Ions from components having the same number of chlorine atoms (e.g., m/z320 and 322) are added to realize even a small improvement of the S/Nratio. Further, the currents of all the ions originating from dioxinsare integrated (sigmaIm) and taken as the total amount of dioxins. Afterone dioxin ion monitoring cycle is complete, monitoring of dioxins isrepeated. The number of repeat measurements may be set by an externaldevice. Integration is performed as required starting from one cycle toimprove the S/N ratio. When measurement of dioxins is complete,measurement of clorobenzenes begins. The sensitivity of the detector isset to medium sensitivity, and the ion introduction time is also set.The ions derived from chlorobenzene in FIG. 31A are monitored one afteranother. The results are integrated for monitored ions having the samenumber of chlorine atoms. In this way, a component distribution forisomers of chlorobenzenes can be calculated. All the ion amounts arealso integrated (sigmaIm10) to calculate the total amount ofchlorobenzenes. After one measurement cycle is complete, monitoring ofchlorobenzenes is performed again and the ion amount is integrated. Thenumber of repeat measurements may be one or more depending on theconcentration. One cycle is completed in about 1 second. Whenmeasurement of chlorobenzenes is complete, monitoring of chlorophenolsbegins. For chlorophenols, the ions shown in FIG. 31B are monitored.Monitoring is repeated as in the case of chlorobenzenes, and thedistribution of components and total amount of chlorobenzenes arecalculated. After measurement of chlorobenzenes is complete, NO_(x),SO_(x), hydrogen chloride and oxygen, etc., are monitored. Aftermeasurements are complete, a comparison with previously measured valuesand mass spectra is made to determine whether an abnormal state exists.If an abnormal state exists, an alarm is output. This monitoring isperformed in an endless loop, and monitoring conditions are changed byexternal devices as necessary.

[0089] Herein, measurements and embodiments were described concerningmainly the dioxin and related compounds in flue gas discharged from agarbage incineration plant. Measurements of dioxins and relatedcompounds in flue gas from a metal refining process and the atmospherecan be made with the same equipment and methods. This monitoring devicemakes it possible to directly know how much dioxins are contained influe gas, such as from an incinerator, and how much fluctuation thereis. It permits real time dioxin monitoring and concentration measurementof dioxins in many locations in an incinerator. After combustion startsin the incinerator, the flue gas passes through a large number ofdifferent areas at different temperatures until it is discharged intothe atmosphere from a flue, and many chemical reaction processes occurin the flue gas before it is discharged. Using this monitoring device,it is possible to follow dioxin formation and decomposition in each ofthese complicated processes. It is of course also possible to acquireinformation for changing and optimizing process conditions aimed atcutting down dioxins.

[0090] In the above-mentioned example, the ions produced by the negativecorona discharge were introduced into the mass spectrometer afterdeflection, although they may of course be introduced into the massanalysis part without deflection.

[0091] Furthermore, although the case was described where an ion trapmass spectrometer was used as the mass spectrometer, other massspectrometers, such as a quadruple mass spectrometer and a compactmagnetic field type mass spectrometer, may also be used.

[0092] (Embodiment 2)

[0093]FIG. 30 shows the general abundance ratio of the main componentscontained in flue gas from a garbage incineration plant. The verticalaxis shows abundance ratio. 1 represents 100%. 10⁻⁶ corresponds to ppm,10⁻⁹ corresponds to ppb, and 10⁻¹² corresponds to ppt. After oxygen,carbon dioxide and water which are present at % levels, carbon monoxideand hydrocarbons are present at a level of 1000 ppm. There are a largenumber of components in hydrocarbons and their concentrations aredistributed over a wide range from 10 ppm to the 1 ppt level. Hydrogenchloride (250 ppm to 1300 ppm), NO_(x) (100 to 200 ppm) and SO_(x) (−100ppm), etc., are present at a level of several 100 ppm. On the otherhand, the concentration of chlorobenzenes and chlorophenols which aresaid to be precursors of dioxin is of the order of 1 ppb (1000 ng/Nm³).The concentration of dioxins is below 10 ppt (10 ng/Nm³). Thus, todirectly measure target components such as dioxin precursors and dioxinsin flue gas, high selectivity is essential to detect only minute amountsof the target components together with many interfering substances whichare present in large concentrations. For this reason, it is veryeffective to use negative corona discharge and to use a massspectrometer for detection of the ions produced. There are some caseswhen substances are present which are ionized by negative coronadischarge in the same way and generate ions of the same ion mass numberas the target components, and in these cases, detection of the targetcomponents alone is very difficult with a mass spectrometer usingnegative corona discharge.

[0094] However, if an ion trap mass spectrometer is used, higherselectivity can be obtained than in an ordinary mass spectrum bydissociating the generated ions (removing certain component elements orgroups from the ions) to convert them to ions of different mass number.This is the MS/MS method wherein, in addition to the high frequencyvoltage applied to the ring electrode 46 and endcap electrodes 45 a, bfrom the high frequency power supply 100, energy is given to the trappedmolecular ions from an auxiliary alternating current voltage applied tothe endcap electrodes 45 a, b from an auxiliary alternating currentpower supply 98, thereby causing the molecular ions to collide with thebuffer gas (e.g., He) in the electrodes so that they dissociate. Inpractice, an alternating current voltage (amplitude less than V, appliedtime of the order of several tens of ms, frequency of the order of 50 to500 kHz) having an identical or slightly different characteristicfrequency to that of the trapped ions is applied to the endcapelectrodes 45 a, b. In the case of an organochlorine compound, ions areobserved by the MS/MS method from which one or two chlorine atoms havebeen eliminated. For example, in the case of 2,4 dichlorophenol, asshown in FIGS. 31A and 31B, the negative ion (M−H)⁻ (M: molecule, H:hydrogen) is produced by negative corona discharge. If this negative ionis dissociated by the MS/MS method, a negative ion is produced fromwhich one chlorine atom has been eliminated. Observing this negative ionmeans observing a process wherein a negative ion is formed from whichone chlorine atom has been eliminated via (M−H)⁻ from M indichlorophenol, and very high selectivity can be obtained. Therefore,dichlorophenol can be detected even if an interfering substance which isionized by a negative corona discharge and produces an ion of the samemass number, exists. In this case, a chromatogram (showing the variationof ion intensity with time) as shown in FIG. 27 is obtained, and if theamount of the negative ion from which one chlorine atom was eliminatedis measured from the intensity of this peak, the amount ofdichlorophenol in flue gas can be estimated. When there are pluralmolecular species to be measured, this measurement process may berepeated. In the case of dioxins, a COCl desorption process is observedin addition to dechlorination. Desorption of COCl is a process observedonly in dioxins, and if this process is observed, it can be said toprove that TCDD or highly toxic dioxins are present. When there areplural molecular species which are to be measured, measurement by theMS/MS method may be repeated, but measurements may also be carried outsimultaneously as follows. Taking chlorophenols as an example, thenegative ions of di-, tri-, tetra- and pentachlorophenol produced bycorona discharge are selectively trapped in the mass analyzing part.This is done by applying a white noise auxiliary alternating currentwhich does not contain the characteristic frequency of the ion group tobe. trapped, to the endcap electrodes 45 a and b, as stated previously.Next, an auxiliary alternating current comprising superimposed auxiliaryalternating currents which are identical to or slightly different fromthe characteristic frequencies of the trapped ions, is applied to theendcap electrodes 45 a, b to supply energy to the trapped molecularions, and ions wherein a chlorine atom has been eliminated from theabove-mentioned negative ions of chlorophenol, are thereby produced. Thesum of the intensities of the ions corresponding to mono-, di-, tri- andtetrachlorophenol corresponds to the total amount of chlorophenols whichis to be calculated.

[0095] In an actual incinerator, in the case of chlorophenols, di-, tri-and tetrachlorophenols account for at least 50% of the total amount ofchlorophenols, therefore the amount of chlorophenols can be representedby the amount of di-, tri- and tetrachlorophenols instead of measuringall the chlorophenols. This reasoning can also be applied tochlorobenzenes and dioxins.

[0096] (Embodiment 3)

[0097] Although measurements can be made continuously at one gassampling point in a garbage incineration plant for a long period oftime, combustion control conditions can be better grasped by increasingthe number of measurement points. FIG. 15 is a schematic view of agarbage incineration plant. Garbage thrown into a hopper 72 is dried,thrown into a furnace 73 having a large number of grates 74, and burntby primary air supplied from underneath. The combustion gases are mixedup in the furnace 73, and burn. Secondary air is blown into thecombustion gases from a secondary air nozzle 75 to complete thecombustion. Next, the hot combustion gases are led to a boiler 76 whereheat recovery is performed. Due to the high temperature of the secondarycombustion resulting from supply of secondary air, most organiccompounds and organochlorine compounds are decomposed. However, althoughorganochlorine compounds decrease, more NO_(x), etc., is generated bythe secondary combustion. If the gas sampling points A and B of thepresent application are provided in this area, the fluctuation in theconcentration of NO_(x), dioxins and organochlorine compounds due tosecondary air injection and combustion temperature can effectively bemonitored in real time. It is thus possible to operate the incineratorso that the occurrence of NO_(x) and dioxins is inhibited. By monitoringa point B before the boiler 76 and a point C after it, information canbe gained regarding the generation and behavior of NO_(x) and dioxinsinside the boiler. Further, if monitoring is performed before and afterthe introduction of adsorbents such as active carbon and slaked lime,the amount of these additions can be geared to higher efficiency, theamounts added can be reduced, and cost reductions can be achieved. Whenmeasurements are performed at a large number of points by time sharing,the flowpath is changed over by a flowpath change-over valve 81 as shownin FIG. 18. In FIG. 18, the case of three measurement points is shown,but the number of measurement points can be increased further. Theoperating state of an actual monitor is shown in FIG. 32. If monitoringof plural points is changed over by the flowpath change-over valve 81with time sharing, one monitoring device is sufficient. To sample atpoint A, the flowpath is changed over to point A. Monitoring iscompleted in about several seconds to several tens of seconds, butmeasurements are repeated to improve the S/N ratio and smooth thesignal. The number of repeat measurements can be set freely as required.When monitoring of point A is completed in several seconds to severalminutes, the flowpath change-over valve is changed over and monitoringmoves on to point B. If there are a larger number of measurement pointsand the time for one measurement is about 30 seconds, even measurementsat ten points can be performed in a cycle of 5 minutes. Also, flue gasshould be made to flow continuously through the piping in the flowpathbeing measured, and through piping in other flowpaths not beingmeasured, to avoid adsorption of components present in small amounts bythe piping system, temperature variations, and pressure variations.

[0098] (Embodiment 4)

[0099] In the case of dioxin measurements in the atmosphere, etc., thedioxin concentration is still less as compared with the flue gas of agarbage incineration plant. It is therefore difficult to detect dioxineven if a sample gas is directly introduced to the ion source. In thiscase, a trap column 83 for trapping dioxin can be inserted in the gassampling path, as shown in FIG. 19. After the dioxins have been adsorbedand concentrated, the flowpath is changed over to desorb the dioxinswhich are then detected. In this case, if high purity nitrogen gas orair in a cylinder 85 is used as a carrier gas for desorption, moisture,carbon dioxide and hydrocarbons, etc., in the gas can be eliminated. Formonitoring substances present in high concentration such as NO_(x) andSO_(x), flue gas may be introduced to the ion source withoutmodification, adsorption and concentration being performed only forcomponents present in minute amounts like dioxins.

[0100] This will be described referring to FIG. 19. Sample gas isextracted by the gas sampling probe 3 inserted in the flue 1, and ash,etc., is removed by the dust filter 20 and the metal filter 23.Chlorobenzenes and chlorophenols, etc., which are present in highconcentration in the sample gas, pass through a three-way cock 82 a,piping and a three-way cock 82 b, and are sent directly to the monitorpart 11 where they are monitored. When dioxins are monitored, thethree-way cocks 82 a, b are changed over. The sample gas then passesthrough piping, a four-way cock 84, the trap column 83 and three-waycock 82 b, and is led to the ion source 30. The dioxins are adsorbed andconcentrated by the trap column 83. When a trap concentration time ofabout several minutes to several tens of minutes has elapsed, thefour-way cock 84 is changed over, and nitrogen gas from the nitrogencylinder 85 is passed through the trap column 83. At the same time asthe four-way cock 84 is changed over, the trap column 83 is rapidlyheated by energizing a column heater 99 surrounding the trap column.Dioxins adsorbed by the trap column 83 are then desorbed, and led to theion source 30 where they are ionized and monitored. For highconcentration components, the gas may be directly connected, whereas tomonitor components present in medium concentration or in very lowamounts, plural trap columns may be prepared and monitoring performedseparately for each component. For example, different trap times may beused, e.g., 10 seconds for medium concentration components and 100seconds for components present in very low amounts.

[0101] (Embodiment 5)

[0102] By using a calibration curve, the ion current measured by themonitoring apparatus is converted into a concentration of a dioxin or anorganochlorine compound. For this purpose, the change-over valve 24 forintroducing a standard sample is periodically changed over as required,or once a day, etc., to introduce a fixed amount of a standard substancetogether with a suitable gas from a chemical cylinder, not shown, or thestandard sample generator 10, and automatic calibration of the monitoris performed. As the standard substance, a volatile organochlorinecompound such as a chlorobenzene or a chlorophenol may be used, orNO_(x), SO_(x), etc., may be used. The signal obtained by introducingthe sample substance is compared with a value which was previously inputor a previously measured value, and if there is a large deviation, analarm is output and calibration is performed.

[0103] (Embodiment 6)

[0104] During on-line measurement or whenever necessary, e.g., once aday, a self-test is performed as to whether there are any abnormalitiesin measured signals, the background, temperature of the flue gas,pressure or flowrate, etc., and required operations, such as automaticcleaning, automatic calibration, issue of device fault alarms or deviceshutdown, are performed.

[0105] (Embodiment 7)

[0106] To detect short-term abnormalities, another process is required.This constantly determines whether or not there are faults, as shown inFIG. 34. The determination may be performed by manually inputting anaverage value for the incinerator from an I/O device beforehand, or byrepeating measurements to automatically calculate an average value. InFIG. 34, a method of automatically calculating an average value is shownby a flowchart. After sequentially determining dioxins, chlorobenzenesand chlorophenols, the value of each component is compared with anaverage value. If the deviation is greater than a predetermined value,an alarm is output by an I/O device or alarm instrument, and measurementis repeated. If the alarm is repeated, a higher level alarm is issued,and self-diagnosis, calibration and monitoring apparatus shutdown areperformed.

[0107] The components causing the abnormal value are likely to becontained in the flue gas, therefore, the trace component monitoringapparatus shifts to a different determining mode from ordinarymonitoring. When there is a fault condition, the mass spectrometerperforms a mass scan to acquire mass spectra. These are then filed andrecorded together with other parameters, and displayed on the I/Odevice. The blow volume of primary air or secondary air supplied to thefurnace is adjusted by the combustion controller 15 while monitoring thesituation, and emission of dioxins, chlorobenzenes and chlorophenols issuppressed. This determination also aids in identifying the cause of theabnormal condition.

[0108] Mass spectra are obtained not only in abnormal conditions. If amass spectrum scan is included in the monitoring cycle for dioxins, andmass spectra are constantly acquired as monitoring is performed, thestate of the furnace can be known at any time. For example, if a largeamount of garbage containing water is incinerated, large peaks due towater ions appear in the mass spectrum, and if a large amount of vinylchloride is incinerated, large peaks due to chlorine ions appear in themass spectrum. If a mass spectrum is periodically interspersed in themonitoring of components present in very small amounts and this massspectrum is observed, an abnormal state can be detected. The measuredmass spectrum is compared with a previously measured mass spectrum(comparison mass spectrum), and if a new mass peak appears or a largemass peak disappears, it is determined that an abnormal state exists.Specifically, the intensities of mass peaks having the same mass/chargeratio (m/z) on the spectra to be compared are subtracted from oneanother. If there is no peak on a mass spectrum, the intensity is takento be 0. If a large peak appears on the difference spectrum, itsignifies a component that has suddenly appeared in the flue gas, sothis is regarded as abnormal and an alarm is output.

[0109] The measured data are processed by data processing, and filed andstored together with set values or experimental values of combustionconditions. If there are parts showing values exceeding the referencevalues, they are color-coded, e.g., with red or pink, and an alarm isimmediately output to the operator. If necessary, the data are output toa printer or CRT, and also sent to an incineration surveillance andcontrol system.

[0110] (Embodiment 8)

[0111] During measurements, flue gas is allowed to flow continuouslythrough the atmospheric pressure ion source and piping to maintain anequilibrium in the exchange of gas and substances adsorbed on the wallsurface, and eliminate adsorption of components present in very smallamounts on the wall surface. When the flow of flue gas is stopped duringshutdown of the incinerator, maintenance inspections or filterreplacement in the sampling system, high purity nitrogen gas isautomatically circulated to prevent soiling of the atmospheric pressureion source or piping. Also, depending on the state of soiling of the ionsource or piping, a purge gas such as a high purity gas is circulated,for example once a week, to perform automatic cleaning of the ion sourceand pipes. When the emission of the standard sample from the standardsample generator 10 in the monitoring apparatus shown in FIG. 1 isstopped, nitrogen gas from a nitrogen cylinder, not shown, is passedthrough the valves, piping and the ion source 30 without modification toperform cleaning. The device is periodically cleaned by allowingnitrogen gas to flow periodically when the device is started or stopped,or during measurement. The nitrogen gas may be introduced into the gassampling unit 88 separately from the standard sample introductionsystem. If flue gas is introduced and measurements are begun afterpassing pure nitrogen through the system, the flue gas is allowed toflow for at least 30 minutes to prevent adhesion to the pipe walls.

[0112] (Embodiment 9)

[0113]FIG. 30 shows abundance ratios for the main components included influe gas. The vertical axis shows the abundance ratio. 1 represents100%. 10⁻⁶ represents ppm, 10⁻⁹ represents ppb and 10⁻¹² represents ppt.After nitrogen, oxygen, carbon dioxide and water which are present at %levels, carbon monoxide and hydrocarbons are present at a level of 1000ppm. Hydrocarbons contain many components, and their concentrations aredistributed over a wide range from 10 ppm to 1 ppt. Hydrogen chloride(250 to 1300 ppm), NO_(x), (100 to 200 ppm) and SO_(x) (−100 ppm) arepresent to the extent of several hundred ppm. On the other hand, theconcentration of chlorobenzenes and chlorophenols which are said to bedioxin precursors, is said to be of the order of 1 ppb (1000 ng/Nm³).The concentration of dioxins is below 10 ppt (10 ng/Nm³). Inorganiccompounds containing highly electronegative elements such as oxygen,sulfur and halogens (F, Cl, Br and I) (nitrogen oxides (NO_(x)), sulfuroxides (SO_(x)), chlorine (Cl₂), hydrogen chloride (HCl)) are alsopresent in flue gas to the extent of several hundred ppm. Thesesubstances are also noxious substances of which the discharge into theatmosphere is regulated. Moreover, by using negative ion modeatmospheric pressure chemical ionization, in addition to thesesubstances, oxygen and water can be ionized and measured in the same wayas dioxins and organochlorine compounds such as chlorophenols andchlorobenzenes.

[0114] NO_(x) and SO_(x) are present in high concentrations 108 to 109times greater than the concentration of dioxins. Therefore, even if theionizing efficiency is somewhat inferior, the amount of such ionsdetected is far greater than that of dioxins, and consequently, it isnot the best policy to measure dioxins, chlorophenol and chlorobenzeneat the same time as NO_(x), and SO_(x). In this case, the mass spectrumof NO_(x) and SO_(x) is obtained at low sensitivity in one mass analysis(one mass scan), the mode is changed over to medium sensitivity andmeasurement of chlorobenzenes and chlorophenols is performed, andfinally, the mode is changed over to high sensitivity and a massanalysis of dioxins is performed.

[0115] There are several methods of changing over the sensitivity. FIG.33 shows the case where the mass spectrometer is an ion trap massspectrometer. By adjusting the time during which ions are introduced toand accumulated in the ion trap mass analyzer from an external device, alarge dynamic range can be covered. When the ion current is small, theion accumulating time is lengthened. Conversely, when there is a largeion current, the ion accumulating time is shortened. After introducingand accumulating ions, a mass scan is performed and a mass spectrum isobtained. The detector is also synchronized, and is switched betweenlow, medium and high gain to perform measurements. If measurements arealternately repeated while switching through the three sensitivities,dioxins, chlorobenzenes, chlorophenols, NO_(x) and SO_(x), etc. caneffectively be measured in real time. Dioxins are present only inextremely low amounts as compared with chlorobenzenes and chlorophenols,or NO_(x) and SO_(x). For this reason, these three groups of substancesare not monitored equally, the number of measurements in one cycle isincreased in the case of dioxins which are present in only very smallamounts, and the data are smoothed. The frequency of monitoring betweenthe three groups may also be varied.

[0116] (Embodiment 10)

[0117] In the above example, the case was mainly described wherenegative ion atmospheric pressure chemical ionization is used. Variouscomponents are present in flue gas, but for hydrocarbon compounds, suchas olefinic hydrocarbons or aromatic compounds typified by benzene,etc., or compounds with low numbers of chlorine atoms, measurements canalso be made by positive ion mode atmospheric pressure chemicalionization. For example, with benzene and monochlorobenzene, the ionspecies M+ is generated by positive ion atmospheric pressure chemicalionization. Other ion species observed in positive ion mode are (M+H)⁺,etc.

[0118] The ions derived from hydrocarbons obtained by the positive ionmode represent the combustion state of the furnace, and may also be usedas an indicator of incomplete combustion like carbon monoxide.Specifically, when ions derived from hydrocarbons with high molecularweight are observed in large quantities, it can be presumed thatcombustion is inadequate. Further, in actual sample gas monitoring, itis also effective to increase the amount of information during gassampling by making measurements alternately in the positive and negativeionization modes.

[0119] (Embodiment 11)

[0120] In the above-mentioned example, the description focused mainly onremoving solids, such as ash, from the dust filter part, but filters mayalso be provided for removing gaseous components present in largeamounts such as hydrogen chloride. In an ordinary incinerator, thecomposition of gas produced by burning garbage may vary. In such a case,it is effective to provide a filter before the monitor part 11 forremoving large amounts of gaseous components and suppressing largefluctuations of gas component composition. For example, in the case ofhydrogen chloride, if a filter filled with calcium carbonate or slakedlime is provided, the level of hydrogen chloride falls to several 100ppm even if it originally exceeded 1000 ppm, so interference with theionization of target substances by a large amount of hydrogen chloridegas is mitigated, and monitoring is made easier.

[0121] Atmospheric pressure chemical ionization using a negative coronadischarge is a high sensitivity, high selectivity ionization techniquewhich can selectively ionize organochlorine compounds or compoundscontaining highly electronegative elements in the presence of largenumbers of interfering substances. By combining this with ion trap massspectrometry, an even more highly sensitive and selective monitoringmethod is obtained. Hence, this application permits direct monitoring ofdioxins, dioxin precursors (chlorobenzenes and chlorophenols) andNO_(x), SO_(x) in flue gas by directly sampling gas from the flue.

What is claimed is:
 1. A monitoring apparatus comprising: a gas samplingunit for sampling flue gas or atmospheric air; an ion source forionizing components present in very small amounts in said flue gas oratmospheric air under atmospheric pressure or a pressure based thereon;a mass analyzing unit, provided in a region evacuated to a pressurelower than atmospheric, for mass analysis of ions generated by said ionsource and measuring their ion current signals; and a data processor forprocessing the measured signals; wherein at least one of dioxins,chlorobenzenes and chlorophenols in said flue gas or atmospheric air ismonitored.
 2. A monitoring apparatus according to claim 1, wherein saidion source is an atmospheric pressure chemical ion source operating in anegative ion mode.
 3. A monitoring apparatus according to claim 2,wherein said analyzing part is an ion trap mass analyzing part.
 4. Amonitoring apparatus according to claim 3, wherein said monitoring isperformed by integrating ion currents derived from isomers of dioxins,chlorobenzenes or chlorophenols.
 5. A monitering apparatus according toclaim 4, wherein said monitored ion species of dioxins, chlorobenzenesor chlorophenols comprises ions based on stable isotopes of the chlorineatom.
 6. A monitoring apparatus according to claim 3, wherein saidmonitored ion species are ions wherein a chlorine atom has been removedfrom M⁻, (M−Cl+O) or orthoquinone ions in the case of dioxins, M⁻ or(M−Cl)⁻ in the case of chlorobenzenes, and M⁻ or (M−H)⁻ in the case ofchlorophenols.
 7. A monitoring apparatus comprising: a gas samplingsystem for sampling flue gas or atmospheric air; an ion source forionizing component present in very small amounts in said flue gas oratmospheric air under atmospheric pressure or a pressure based thereon;a mass analyzing part, provided in a region evacuated to a pressurelower than atmospheric, for mass analysis of ions generated by said ionsource and measuring their ion current signals; and a data processor forprocessing measured signals; wherein at least one organic or inorganiccompound containing at least one element from Group VI or Group VII ofthe periodic table such as oxygen, sulfur or halogen in the molecule ofsaid component, is monitored.
 8. A monitoring apparatus according toclaim 7, wherein said organic compound is at least one of dioxins,chlorobenzenes or chlorophenols.
 9. A monitoring apparatus according toclaim 8, wherein said inorganic compound is at least one of nitrogenoxides (NO_(x)), sulfur oxides (SO_(x)), hydrogen chloride (HCl),chlorine (Cl₂) or oxygen (O₂).
 10. A monitoring apparatus according toclaim 9, wherein the measurement of said inorganic compound and themeasurement of said organic compound are performed separately on a timesharing basis.
 11. An incinerator, wherein a sample gas is directlyintroduced to an atmospheric pressure ion source via a pipe, and atleast one component of dioxins, chlorobenzenes or chlorophenols ismonitored by ionizing components present in very small amounts in saidsample gas and performing mass analysis.
 12. A method of monitoringchemical substances comprising the steps of: sampling a gas containinghydrocarbons; separating a sample gas from said gas, a first introducingstep for introducing said separated sample gas to an ionizing unit;ionizing and producing ionized substances by subjecting said introducedsample gas to a discharge, a second introducing step for introducingsaid ionized substances to an ion trap analyzing part; and detecting anion current of predetermined ionized substances.
 13. A method ofmonitoring chemical substances comprising the steps of: sampling a gascontaining hydrocarbons; separating a sample gas from said gas, a firstintroducing step for introducing said separated sample gas to anionizing unit; ionizing and producing ionized substances by subjectingsaid introduced sample gas to a discharge, a second introducing step forintroducing said ionized substances to an ion trap analyzing part; anddetecting a mass of predetermined ionized substances.
 14. A method ofmonitoring chemical substances according to claim 12 or 13, wherein anion trap mass spectrometer is used as said ion trap analyzing part. 15.A method of monitoring chemical substances comprising the steps of:sampling a gas comprising hydrocarbons; separating a sample gas fromsaid gas, a first introducing step for introducing said separated samplegas to an ionizing unit; ionizing and producing ionized substances bysubjecting said introduced sample gas to a discharge, a secondintroducing step for introducing said ionized substances to an ion trapmass analyzing part; producing ion substances wherein an atom is removedfrom the ionized substances introduced in said second introducing step;and detecting an ion current of said ion substances.
 16. A method ofmonitoring chemical substances comprising the steps of: sampling a gascomprising hydrocarbons; separating a sample gas from said gas, a firstintroducing step for introducing said separated sample gas to anionizing unit; ionizing and producing ionized substances by subjectingsaid introduced sample gas to a discharge, a second introducing step forintroducing said ionized substances to an ion trap mass analyzing part;producing ion substances wherein either an atom or molecule has beenremoved from the ionized substances introduced in said secondintroducing step; and detecting an ion mass of said ion substances. 17.A method of monitoring chemical substances comprising the steps of:producing ion substances wherein a hydrogen atom has been removed fromdioxin precursors in flue gas; introducing said ion substances to an iontrap mass spectrometer; producing negative ions wherein a chlorine atomof the dioxin precursors is selectively removed from said ionizedsubstances; and measuring an amount of the negative ions produced.
 18. Amonitoring apparatus comprising: a sampling pipe having a sampling portfor sampling a gas; a first filter for removing impurities from saidsampled gas; an ionizer for ionizing sample gas which has passed throughsaid filter by a discharge; a second filter for removing microparticlesfrom ionized substances; a mass spectrometer which dissociates achlorine atom from the ionized substances which have passed through saidsecond filter; and an ion/charge converter for measuring the current ofthe remaining ions.
 19. An incinerator comprising: a garbage hopper; afurnace for burning said garbage; a gas supply nozzle for supplying gasto the interior of said furnace; a boiler for recovering heat from saidincinerator; a flue for discharging flue gas which has passed throughsaid boiler; a sampling port for sampling flue gas from either or bothof said gas supply nozzle or said boiler; an ion source for ionizing gasfrom said sampling port by a discharge; a measuring device for measuringa predetermined target substance contained in said flue gas from theionized substance from said ion source; and a controller for controllingthe temperature of said incinerator by the measured results.
 20. Anincinerator comprising: a garbage hopper; a furnace for burning saidgarbage; a gas supply nozzle for supplying gas to the interior of saidfurnace; a boiler for recovering heat from said incinerator and a fluefor discharging flue gas which has passed through said boiler; asampling port for sampling flue gas from either or both of said gassupply nozzle or said boiler; an ion source for ionizing gas from saidsampling port by a discharge; a measuring apparatus for measuring apredetermined target substance contained in said flue gas from theionized substance from said ion source; and a display device fordisplaying flue gas sampling points of said incinerator, displayingmeasured results at said sampling points, and outputting an alarm whensaid results exceed predetermined values.